The morphological change in collagen fibers of the periodontium is one of the most striking features of periodontal disease. Detailed structural studies of human gingival collagen, both soluble and insoluble, from healthy and diseased tissues are proposed at the molecular level (tropocollagen), at the subunit level (alpha-, beta- and gamma- chains) and at the CNBr-peptide level. Insoluble collagen will be solubilized by treatment with CNBr or with pepsin at low temperature. Viscometry, ultracentrifugation and electron microscopy of SLS- crystallites will be used for molecular characterization. Chromatographic separation, disc electrophoresis, amino acid analysis, determinatton of carbohydrate content and amino acid sequencing of certain peptides (believed to be involved in the pathologic process) will be used to characterize the peptides. Immunological studies will determine the relative antigenicity of gingival collagen and the role of the telopeptides as sites of antigenic determinants in healthy and diseased gingiva. These structural and immunological studies will be correlated with the histological and clinical observations to establish the molecular basis of connective tissue disorder in periodontal disease. Thus, the state of collagen fibers in human gingiva may serve as a parameter to assess the progress of a pathologic condition.